I have no idea whether anyone out there might be interested in this -- but I got a Vivitar 300mm telephoto lens as a part of an auction site win. It was supposed to have a Nikon mount, but it doesn't -- it says M/SR at the base, which I believe means that it mounts to Minolta SRT or possibly a Konica.

This is a manual focus lens -- it is in very good shape, with no scrathes or haze and some minor dust. Comes with caps and a built in hood.

I guess there is an adapter out there for this for an M42 mount, but I'm not sure.